1. Field of Invention
The present invention relates to a projection type display, a display and a drive method thereof. In particular, it relates to a projection type display, a display and its drive method, that are superior in an image expression and obtain an image of brightness fitted for a user's favorite and an operating environment.
2. Description of Related Art
The related art includes developments in information apparatuses. In the related art, there is an increasing demand for flat type displays with high resolution and low power consumption. Thus, the related art includes research and development of these features. In particular, a liquid crystal display is expected to satisfy the above-mentioned demand since its optical characteristic varies by electrically controlling an alignment of liquid crystal molecules. As one form of this liquid crystal display, a projection type liquid crystal display (liquid crystal projector) is well known. The display projects and enlarges an image emitted from optical system using a liquid crystal display light valve onto a screen via a projection lens.
A projection type liquid crystal display uses a liquid crystal light valve as a light modulation device. On the other hand, projection type displays in practical use include those using a digital mirror device (hereafter “DMD”) as a light modulation device in addition to a liquid crystal light valve. However, this kind of a related art projection type display has the following problems.
(1) Sufficient contrast cannot be obtained because of light leakage and stray light among various kinds of optical elements constituting an optical system. Hence, the range of gray scale for displaying (the dynamic range) is narrow, and the related art projection type display is inferior to an existing monitor using a cathode ray tube (hereafter “CRT”) in quality and strong appeal of an image.
(2) Even if improvement in quality of an image is intended by processing various kinds of image signals, sufficient effects are not exhibited because of the narrow dynamic range.
In order to address or solve such problems of a projection type display, namely in order to expand its dynamic range, it is considered that a flux of light incident on a light modulation device (a light valve) is changed in response to an image signal. The most convenient method to realize such change is to change the light-emitting intensity of a lamp. Japanese Patent Laid-Open No. 3-179886 discloses a method to control the light-emitting intensity of a metal halide lamp.
As a lamp used in a projection type liquid crystal display, a high-pressure mercury lamp is commonly used in the related art. However, it is extremely difficult to control the light-emitting intensity of a high-pressure mercury lamp. Hence, it is required to provide a method that changes a flux of light incident on a light modulation device in response to an image signal, even if the light-emitting intensity of a lamp itself is not changed.
In addition to the above-mentioned problems, the light-emitting intensity of a light source is fixed in related art projection type displays. Hence, it is a problem that, for example, a displayed image becomes too bright under a viewing environment that is relatively dark, and brightness of a displayed image changes in response to the size of a projection screen changed by zooming a projection lens and a projection distance.
In order to overcome the above mentioned problems, the object of the present invention is to provide a projection type display, a display and its driving method that can change a flux of light incident onto a light modulation device without changing the light-emitting intensity of a lamp and show superior effects in an image expression and adaptability to an operating environment.